What s the best Class A integrated tube amp over 80W

I read that biasing VT100 tubes is a big headache. Why is it such a headache?

I read that biasing VT100 tubes is a big headache. Why is it such a headache?

I’ve heard the VT100 a few times but never biased it so I do not know the process. But one of the tube amps I have is a Canary 301 mk 2. To bias the Canary, I need to flip the amp and remove the bottom cover. Then with a volt meter, put the probes on specific locations in order to bias each power tube. The first few times I did this convinced me to sell the amp. But I missed the Canary so  I purchased one again. Now that I’m more familiar with biasing the amp, its not an issue for me. I set the bias only once per year and that’s good enough. Canary has since made biasing procedures easier on all their amps.  I like easy biasing but sometimes you can’t have everything. Also, most of my amps are very easy to bias so if I have 1 or 2 that involve a little skill, I can live with that and it makes this hobby even more interesting. 

@chungjh ... do a search in the Forum for old posts about the ARC VT 100.  I recall that some years back, a couple of techie members explained why biasing the VT100 is so hard, ... and a tad dangerous for non-experienced, non-techies. 

I don't recall if you mentioned your budget, but someone mentioned the ARC Ref 150SE as a possibility.  I own that amp and it is a stunner.

I have question for you that should be answered by a techie.  If your ESLs have an impedance of 30 ohms in the low end of the spectrum and 3 ohms in the treble, is a tube amp a good choice for you?  Your ESLs operate almost like a giant capacitor.

I ask because many tube amps have high'ish output impedances.  Even the Ref 150SE has a "low'ish" (for a tube amp) .55 output impedance off the 4 ohm taps in the bass region; the amp's output impedance creeps up with frequency. 

I mention this because a tube amp's output impedance may color the sound based on Ohm's Law principles.  See, e.g., John Atkinson's bench test report on Ref 150 at: 
Audio Research Reference 150 power amplifier Measurements | Stereophile.com   

Based on the impedance figures you mentioned, I calculate that if you used the REF 150SE as your amp, the treble could be shelved down by approximately 2 db as compared to the bass.  Check with a techie.  You could even call ARC customer service. 

Or, if Ralph Karsten (Atmasphere) catches this thread, perhaps he could weigh in.  Ralph manufactures high quality OTL tube amps.  I recall that Ralph posted a while back that he uses his amp to drive ESLs.  Maybe Ralph could explain the whole impedance matching business. 

Good luck with your search.

Bruce
       

I have talked to Ralph (AS) about this. SS output doubles with every doubling of impedance. Therefore my Pass Labs X250.8 SS amp produced about 60W at 30HZ with 30 ohm impedance. On top of that bass frequency takes more power to make the sound than treble. Therefore, Soundlabs sounds too bright at treble with most SS and sounds better with tubes which don't double output with halving of impedance.

I don't know why but I don't know anyone who uses an ARC amp with SL but many who use Atma Sphere amps.